A conventional retractable blade utility knife and its adjustment mechanism is illustrated in FIG. 1. Utility knife 10 comprises a pair of mating housing components 12 which are fastenable together to form a generally hollow interior space and an exterior surface which is contoured to facilitate grasping of the handle. Generally right-angled rails 15 are formed in the housing components to permit sliding of blade carrier 14 for adjustment of blade 16 between a retracted safety position and one or more exposed cutting positions. Blade carrier 14 includes resilient arm member 18 having lateral crosspiece 20 at its terminal end. Lateral crosspiece 20 is engageable in one of a plurality of recesses 22 provided in the housing components to hold the blade in one of a plurality of positions. Adjustment member 24 includes manual interface button 26 connected to shank 28, which is rigidly mounted on resilient arm member 18 of the blade carrier.
As shown more clearly in the enlarged view of FIG. 2, shaft 28 of the adjustment member has a narrower tab 30 which is received through a mating bore in resilient arm member 18 of the blade carrier. During assembly of the utility knife, after tab 30 has been passed through the bore, its bottom surface is stamped or otherwise splayed or enlarged to rigidly mount adjustment member 24 on resilient arm member 18.
Adjustment of blade carrier 14 and blade 16 between a retracted safety position and one or more exposed cutting positions is achieved by exerting a downward force on adjustment member 24 to disengage lateral crosspiece 20 from one of the recesses 22 and sliding adjustment member 24 to position lateral crosspiece 20 in another of the recesses. When the downward force on the adjustment member is released, the lateral crosspiece is engaged in another of the recesses. In this fashion, adjustment of blade 16 to a variety of positions is made possible by depressing, sliding and releasing the adjustment member mounted on the blade carrier. Many utility knives of this general type are known in the art, and various improvements have been made thereon. Some exemplary retractable blade utility knives and improvements are taught in U.S. Pat. Nos. 3,107,426 and 4,586,256, which are assigned to The Stanley Works.
Although prior art utility knives provide generally satisfactory performance in most respects, one important disadvantage is that the adjustment mechanism frequently breaks off from the resilient arm member of the blade carrier. With each adjustment of the blade from a retracted to a working position and vice versa, substantial forces are exerted on the adjustment member and the resilient arm member of the blade carrier. These forces create large stresses at the rigid attachment of the adjustment member to the blade carrier and, over prolonged periods of use, the adjustment member may crack or break and become detached from the blade carrier. With utility knives of the type described above, no provision is made for replacement of the adjustment mechanism and the entire utility knife must be discarded and replaced when the adjustment member becomes detached from the blade carrier or breaks. Since utility knives are commonly used in many industries, the costs involved in replacing utility knives are very large.
Accordingly, it is an objective of the present invention to provide a replaceable adjustment mechanism which is rigidly mountable in a bore of a receiving structure.
It is another objective of the present invention to provide a replaceable adjustment mechanism which is substantially rigidly mountable on the blade carrier of a retractable blade utility knife or the like to extend the useful operating life of the utility knife.
It is yet another objective of the present invention to provide an improved retractable blade utility knife have a replaceable adjustment mechanism to extend the useful operating life of the utility knife.